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#16
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Re: pic: FRC973 Presents Emperor Swerve
No mini-bot?
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#17
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Re: pic: FRC973 Presents Emperor Swerve
Very impressive Adam, this is incredible.
The design is clean, simple, and very well executed. Pulling off both translation and rotation at once is very impressive. A swerve of this caliber has real competitive advantage (as compared to 60% of the swerves that get built). I hope they give you 4 window motors next year so you can do this. |
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#18
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Re: pic: FRC973 Presents Emperor Swerve
Kaiser Krab?
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#19
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Re: pic: FRC973 Presents Emperor Swerve
Nah, that's the same level as King Krab.
So how close is Emperor Swerve to unicorn drive? |
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#20
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Re: pic: FRC973 Presents Emperor Swerve
King Krab? Emperor Krab?
You need a Demo-Krab or Aristo Krab. (HA, I'm funny). Adam, did you guys end up using the shifting on the crab drive? Was it worth it? |
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#21
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Re: pic: FRC973 Presents Emperor Swerve
It is a "Unicorn" drive. 4 motor drive and 4 motor steering with infinite rotation.
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#22
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Re: pic: FRC973 Presents Emperor Swerve
Quote:
I like how the crab drive required minimal CNC work. Was the main coaxial shaft split up into plates? If so, you could easily call them poker chips because that's what they'd look like. What was the hardest part of the crab modules manufacturing implementation? |
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#23
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Re: pic: FRC973 Presents Emperor Swerve
<draw hits floor>
Seriously, that is an impressive machine. Can't wait for pics of the elevator. I am curious what you did as far as programming the drive system is concerned. Someone must have spent a lot of time with vectors.... |
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#24
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Re: pic: FRC973 Presents Emperor Swerve
Quote:
Also, Mecanum and Holonomic/Killough drives, if programmed properly can translate and rotate at the same time. I've seen some FRC robots do it before (2008 comes to mind), but never in full circles (really no reason to, not to mention that it's really hard to keep a constant radius while doing so.) Last edited by thefro526 : 28-09-2011 at 13:07. |
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#25
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Re: pic: FRC973 Presents Emperor Swerve
I spy with my little eye, a window motor in each module. I'm guessing those are for rotating the individual wheels.
What diameter wheels are being used on this"? It appears that they couldn't be much bigger than 4" Of course, smaller wheels makes for smaller modules and less gearing so that would make sense. |
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#26
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Re: pic: FRC973 Presents Emperor Swerve
Quote:
It's definitely been done. Not often, but I've definitely seen it. -Brando |
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#27
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Re: pic: FRC973 Presents Emperor Swerve
Quote:
Edit: Here are two -- http://www.youtube.com/zorkinian#p/a/u/0/Jr-eglZBAHQ http://www.youtube.com/zorkinian#p/a/u/1/sM8cixsE5fo Last edited by Madison : 28-09-2011 at 13:43. |
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#28
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Re: pic: FRC973 Presents Emperor Swerve
Yes it shifts, we're so into the style of robots we've been building that there is no way we could give up shifting. It wasn't much work to integrate at all, just a little more weight.
We prefer to cal it a Emporer Swerve or West Cost Swerve instead of Unicorn Drive, Unicorn Drive's can't shift after-all ![]() The entire mechanical design focused on making programming/controls easier, and there are some cool features we plan to implement. Currently the separate incremental encoder and zeroing sensor allow us to never have to zero sensors by hand, or in code. We also plan to have code that detects an encoder failure, locks that wheel straight, and switches to a drivemode without strafe but still the ability to translate forward/back and steer (We had similar functionality on our arm this year). We really are aiming to make this as reliable as possible. Quote:
The main coaxial shaft is actually a very simple lathe part, it's got less operations than the parts you make in the intro to machining classes here at Cal Poly. The Only CNC'd part I believe is what we call the module tophat. We could have made them on our mill, but wanted to pocket them and there are also a few tight tolerances on them. We also don't really count 2d (Water/laser) cutting as CNC as the time investment involved is vastly different. |
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#29
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Re: pic: FRC973 Presents Emperor Swerve
I derived the steering equations, and they actually converged to exactly what Ether had posted in his whitepapers. This makes sense, as it's the same physical system, but it was really cool to see.
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#30
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Re: pic: FRC973 Presents Emperor Swerve
By now the inverse kinematics1 of mecanum or Unicorn are well known in the CD community. Their 3 degrees of freedom are translation forward/reverse, translation sideways, and rotation. All possible motions or maneuvers can be commanded in terms of these 3 inputs. To rotate while driving forward, for example, all that is required is a field-centric "forward" command (which gets converted into separate time-varying robot-centric forward/reverse and sideways commands) plus a rotate command. The devil is in the details though. Unless the vehicle is built with craftsmanship and attention to detail, it will drift off course due to friction and motor performance tolerances. Encoders can be added to the gearboxes to provide closed-loop control of wheelspeed and/or position to help mitigate these variations, but doing so adds extra complexity and failure modes. For swerve especially, the interaction between steering angle and wheel speed requires careful design of the software to help the driver avoid sudden commands that could in some cases actually result in the vehicle tipping over. So that's the challenge, and it's one of the reasons why teams who want to try their hand at swerve do so off-season. Looks like Team 973 has engineered and crafted a fine specimen. It will be fun to see it perform. 1 given a desired vehicle motion, convert that into the required 4 wheel speeds (for mecanum) or the required 4 wheelspeed/steeringAngle pairs (for swerve) Last edited by Ether : 28-09-2011 at 14:23. |
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